As major media companies have been gathering to start their own cross-media measurement venture and companies like Omniture (NSDQ: OMTR) and Quantcast see their profiles rise, Nielsen media execs want to make sure their clients don’t think they’re getting left behind. The audience measurement company has reached out to about 75 advertisers, agencies and media companies for a private meeting outlining Nielsen’s plans to combine TV and online audience data, B&C reports.

In the client letter, which was sent out Tuesday, Sara Erichson, Nielsen’s president for media client services, North America, said the company will address the implications of TV Everywhere, “OnDemand Online